In these years, as to particulate matter (PM) and nitrogen oxide (NOx) contained in exhaust gas exhausted from internal combustion engines such as diesel-engines, the necessity of purging them is high because of the problem of environment pollution such as acid rain and photochemical smog.
Accordingly, there is conventional technology in which, in the exhaust system of an internal combustion engine, a reducing agent or a reducing agent precursor such as urea water is supplied by spraying to exhaust gas via a reducing agent, etc., supplying nozzle from upstream of an SCR muffler having a selective reduction SCR (Selective Catalytic Reduction) catalyst, thereby selectively reducing and purging nitrogen oxide (NOx) contained in exhaust gas by the SCR catalyst. See, e.g., Japanese Patent Application Laid-Open Publication No. 2001-20724.
Furthermore, there is a system in which an air hole such as a punching hole is formed in an exhaust pipe to disperse and make the flow of exhaust gas uniform. See, e.g., Japanese Utility Model Application Laid-Open Publication No. H02-115912.
However, with such conventional technology, there is the problem that due to the flow of exhaust gas being in a poor condition, the efficiency of purging nitrogen oxide (NOx) is low at the time of transient operation and also, the efficiency is low in the entire range of a low temperature to a high temperature.
In particular, with the case of supplying urea water as a reducing agent precursor, there is also the problem that since the flow of exhaust gas is in a poor condition, urea precipitates in an exhaust pipe, etc., located upstream of an SCR catalyst, thus greatly lowering the efficiency of purging nitrogen oxide (NOx).
Moreover, with conventional technology, there is the problem that since a reducing agent, etc., supplying nozzle is influenced by vibrations of the vehicle, exhaust gas, and the like to vibrate, it is difficult to supply, by spraying, a reducing agent or a reducing agent precursor such as urea water to exhaust gas in such a way that it is dispersed uniformly, and that the efficiency of an SCR catalyst purging nitrogen oxide (NOx) is low.
Also, there is the problem that because of such vibrations caused by vibrations of the vehicle, exhaust gas, and the like, a reducing agent, etc., supplying nozzle is subject to damage and deformation and is low in durability.